The present invention relates to an image reading unit and an image reading apparatus using the same. More particularly, the present invention relates to an image reading unit in which a circuit board is provided with an image sensor for reading image data, a heat dissipating member for controlling a temperature of the image sensor is provided on one side of the circuit board, and a shield member for reducing a noise is provided on the other side and connected to the heat dissipating member via a heat conductive member.
As shown in FIG. 16, a conventional image reading apparatus for reading an image on a document with various sizes as image data includes a light source 86 for irradiating light to the document; a plurality of reflecting mirrors 83, 84, 85 for deflecting the light from the document; a condenser lens 87 for condensing the light reflected by the reflecting mirrors 83, 84, 85; and an image sensor 80 for detecting the light from the condenser lens 87. The light detected by the image sensor 80 is subjected to the photoelectric conversion, and then processed as the image data.
The image sensor for converting the received light into an electric signal reads the image with timing in synchronization with a clock signal with a predetermined frequency. Upon reading the image signal from the image sensor, noises in a frequency band including the clock signal frequency and frequencies with an integral multiple of the clock frequency are generated.
Therefore, in order to prevent the noise from leaking outside, for example, as disclosed in Japanese Patent Publication (KOKAI) No. 05-347685 and Japanese Patent Publication (KOKAI) No. 08-32762, a shield cover made of a metal is provided for covering a periphery of a circuit board.
However, the shield cover is provided to cover not only the circuit board to which the image sensor is attached, but also a larger area including a periphery of the circuit board and the lens, resulting in a large shield cover. Thus, there has been an example that the shield cover covers only the circuit board.
In general, as shown in FIG. 16, the image sensor 80 is attached on the circuit board 81 such that a position of the image sensor 80 with respect to an optical axis can be adjusted by screws or the like. Then, the circuit board 81 provided with the image sensor 80 is fixed to a frame 92 disposed in a chassis of an apparatus main body by using a fixing member 90 such that the image sensor can properly receive the light from the condenser lens 87. A screw 91 fixes the circuit board 81 at a proper position with respect to the condenser lens 87. Then, the shield cover 82 covers the circuit board 81 in order to prevent the noise.
Further, since the image sensor is formed of several millions of electric elements arranged on a silicon board to be a large scale integrated circuit (LSI), a large amount of electricity is consumed, and a heat generation rate per unit-hour becomes high. Especially, in recent years, the number of pixels of the sensor in the image reading apparatus has been steadily increased to achieve a higher-density and higher-speed image reading. The clock speed has been also accelerated in order to achieve higher-speed image data transmission. Consequently, as the image sensor generates more heat, a heat sink or heat dissipating plate needs to be attached to an outline package of the image sensor in order to dissipate the heat generated by the image sensor.
Therefore, in the conventional image reading apparatus, it is necessary for the circuit board to separately provide with a fixing and supporting member for attaching the circuit board to a frame of the apparatus main body, a shield cover for preventing the noise from entering the circuit board or shielding an external noise, and a heat dissipating member (a heat sink member) for dissipating the heat. Therefore, the number of parts increases, and a manufacturing operation becomes cumbersome, resulting in a higher manufacturing cost.
Also, a precise positioning is required for attaching the circuit board to the frame of the apparatus main body, so that a cumbersome adjustment operation is required.
The present invention has been made in view of the aforementioned problems, and an object of the invention is to provide an image reading unit and an image reading apparatus using the same, in which an image sensor and a circuit board are attached to a shield member for shielding and dissipating the heat, so that the number of the parts and manufacturing cost can be lowered while a position of the circuit board is easy to adjust.
Further objects and advantages of the invention will be apparent from the following description of the invention.